It is well known to use a saw blade, such as a bandsaw blade, to cut materials to a desired size. During cutting, material is removed by a series of teeth formed into one edge of a steel strip which makes up the saw blade. FIG. 1 illustrates an example of a bandsaw blade 16 having a group 15 of teeth 10 where each a tooth 10 is defined by a face portion 11 and a back portion 12 that form a tooth point 13. The teeth 10 are spaced from each other at predetermined and substantially equal spacing intervals P1 between successive tooth points 13, often referred to as tooth pitch. The teeth 10 on this type of bandsaw blade 16 are commonly referred to as “straight pitch.” In use, the teeth 10 on the edge of the blade 16 travel across a material to be cut at a predetermined speed. As a result, the blade removes a sliver of material corresponding in thickness to the rate at which the blade 16 passes through the material and the spacing between successive tooth points
The teeth on a bandsaw blade can also be arranged in a recurring pattern on the blade where the teeth within the recurring pattern are disposed at different or variable spacings relative to each other (e.g., variable spacing or variable pitch among the tooth points). The tooth spacing in such a case is referred to as a variable pitch tooth spacing. For example, referring to the bandsaw blade 20 of FIG. 2, the teeth 22 are arranged in a recurring pattern on the saw blade 20 such that the pattern of teeth 22 defined along pattern length 24 of the saw blade 20 repeats along an entire length of the saw blade 20. Additionally, each tooth is disposed on the saw blade 20 at a relatively variable pitch such that each tooth spacing PL and D1 through D6 is unique within the recurring pattern of teeth (i.e., PL≠ D1≠D2≠D3≠D4≠D5≠D6). Both variable pitch and straight pitch blades have advantages and disadvantages when compared to each other. For example, variable pitch blades have been shown to offer reduced vibration and noise relative to straight pitch blades. On the other hand, straight pitch blades have been shown to offer improved cutting life over variable pitch blades when noise and vibration are not present.
As illustrated in FIG. 3, in certain bandsaw blades 30, some of the teeth 32 are bent in a direction normal to a midplane 31 of the saw blade 30. The operation of bending the teeth is referred to as “setting.” During setting, the bent teeth may be arranged in recurring patterns, usually beginning with a non-bent tooth R, often referred to as a raker tooth. The raker tooth R is followed by alternately bent teeth 33 and 34 such that the combination of the raker tooth R and the bent teeth 33, 34 represents one repeat of the recurring pattern 35 between raker teeth. The raker tooth R is often provided with the largest tooth spacing PL in the recurring pattern 35 to make it easier for manufacturing to identify which tooth to reference when performing the setting operation (e.g., to minimize accidental setting or bending of the raker tooth).
In many variable pitch bandsaw blade designs, the volume of material removed during cutting varies from one side of the blade to the other side. The volume of material removed is related to the accumulated pitch of the bent teeth in the pattern where some teeth are bent to one side of the blade and some are bent to the opposite side of the blade. For example, as shown in FIG. 3, adjacent bent teeth 33, 34 are set in opposing directions where a first group of set teeth 33 are bent toward the first side of the blade 36 and a second group of set teeth 34 are bent toward the second side of the blade 38, relative to the midplane 31. With reference to FIGS. 4A and 4B, when the combination of a non-bent raker tooth R and alternately bent set teeth 33, 34 pass through a work piece 40, the tooth points remove material and create a slot or kerf K for passage of the bandsaw blade 30 through the material that is wider than a thickness 42 of the blade 30.
The purpose of the raker tooth R has traditionally been to stabilize the band and prevent the uneven forces generated by the bent teeth 33, 34 from causing the blade 30 to move or cut away from an intended cut plane. In a variable pitch blade, it is common practice to make the spacing in front of the raker tooth R the largest space in the recurring variable pitch pattern. For example, in FIG. 2 the tooth spacing PL, which is directly in front of the raker tooth R, is the largest tooth spacing in the pattern along pattern length 24. By creating the spacing in this manner, the raker tooth R removes more material during cutting than the bent or set teeth.
FIG. 4C illustrates the removal of material by a bandsaw blade 30 during a cutting operation. The thickness of a layer removed from a work piece 40 by a tooth point during cutting is termed chip thickness. Chip thickness t may be calculated by dividing the feed rate F, defined as the progression of the blade 30 through the work piece 40 in inches per minute, by the speed C of the bandsaw blade 30 in inches per minute. The result is then multiplied by the spacing between adjacent tooth points P in inches. The resulting formula is t=P*(F/C) where the chip thickness t is expressed in inches. Because the raker tooth R has the greatest spacing between its tooth point and the point of the adjacent tooth (e.g., the pitch PL as shown in FIG. 2 and FIG. 3) in the variable pitch pattern, the raker tooth R takes the greatest chip thickness t and provides improved guiding and clearing performance. Subsequent bent, or set, teeth 33, 34 take a chip thickness t that is generally smaller than the chip thickness t taken by the raker tooth R due to the smaller pitch (i.e. smaller tooth point spacing) between adjacent bent teeth 33, 34.